[georgemk]

@rmbelson

Are you using the DeDRM plugin like the OP was? And if so is it up to date? It should be at version 6.8.

if you really want to set up the variable then the second post gives you it's name and its value. Just click the "new" button on the Environment Variables page as the link explains and add the new name as per the second post and its value of 1. No need for anything else.

But I repeat, do you have the IDENTICAL issue with the DeDRM plugin and if so have you updated that?

As to what has changed? Did you upgrade Calibre but forgot to check that all the plugins were updated too? Or did Windows upgrade itself? Modern software is complicated so any moving part can cause issues when there is a change.